Winding devices are very common and useful for winding up and unwinding electrical cables, such as power supply cables. Conventional uses include vacuum cleaners with connection cables that can be pulled out of the housing and which are automatically retracted into the housing of the appliance after use and when a winding stop is released. Another example is a unit for programming robots wherein an electrical cable, whose unwindable end is connected to an operating unit, can be pulled out from a computer-connected operating console far enough to allow the operator to leave the moving range of the robot with the operating unit connected to the cable. The cable leaves the operator enough freedom to move around the robot outside the moving range of the robot.
Winding devices of the type described above either work horizontally with a horizontally arranged cable coil, or vertically with a vertically arranged cable coil. In the former case, the cable coil is supported on a supporting disc device. In the latter case, the cable coil can be held between two vertical supporting discs.
In conventional winding devices of the type described above, the supporting disc revolves with the outer drum so that only the hub remains stationary during winding and unwinding. During unwinding, an increasing proportion of the cable coil is wound around the outer circumference of the stationary hub. During the winding process, an increasing proportion of the cable coil is wound around the inner circumference of the rotatable drum. Whenever the cable is being wound or unwound, the cable coil will be wound either around the hub or the circumference of the rotatable drum. A part of the cable will always be in the transitional area between the cable section wound up on the hub and the cable section wound up on the rotatable drum. Since the entire supporting disc turns with the rotatable drum, friction occurs between the supporting disc and the cable coil, dragging along the cable. In other words, due to friction, the rotating supporting disc tries to entrain the cable it supports. This has a positive effect when the cable is wound up on the drum, as a part of the cable wound on the drum is supported to move with the drum, but has a negative effect on the part of the cable wound on the stationary hub and on the part of the cable in the transitional area between the part of the cable wound on the hub and the part of the cable wound on the rotatable drum. The frictional dragging effect leads to buckling of the cable and the formation of undesirable loops, in particular in the transitional area. Such buckles and loops exert an undesirable mechanical stress on the cable. The loops may even fill the radial area between the part of the cable on the hub and that on the rotatable drum, to such an extent that the winding or unwinding process will be impaired.
There is a need for a device that allows the winding and unwinding of a cable but minimizes the frictional dragging effects, buckling and mechanical stress.